X-ray background synthesis: the infrared connection

We present a synthesis model of the X-ray background based on the cross-correlation between mid-infrared and X-ray surveys, where the distribution of type 2 sources is assumed to follow that of luminous infrared galaxies while type 1 sources are traced by the observed ROSAT distribution. The best ¯ts to both the X-ray number counts and background spectrum require at least some density evolution. We explore a lim-ited range of parameter space for the evolutionary variables of the type 2 luminosity function. Matching the redshift distribution to that observed in deep Chandra and XMM-Newton ¯elds, we ¯nd weak residuals as a signature of Fe emission from sources in a relatively peaked range of redshift. This extends the recent work of Franceschini et al., and emphasizes the possible correlation between obscured AGN and star-forming activity. Key words: di®use radiation { X-rays: galaxies { infrared: galaxies { galaxies: active { galaxies: evolution